In mass measurement, vibration, atmospheric pressure, temperature, humidity, static electricity, magnetism, gravitational acceleration, etc., have been considered as error factors (disturbance).
Here, changes in atmospheric pressure, temperature, humidity, and gravitational acceleration out of the above-described error factors occur relatively gradually due to motion of heavenly bodies and weather changes, and have a dominant effect on the volume balance, mass balance, and the like, and an effect in terms of the performance of a weighing device appears as zero-point drifting over a long time. This problem can be solved by a zero-point operation before weighing except when the same sample is continuously measured for a long time.
On the other hand, for the error factors of vibration, static electricity, and magnetism, methods for actively eliminating or removing the factors have been established, such as providing a vibration removal, vibration isolation, or neutralization mechanism, distancing the source of magnetism, and carrying out magnetic shielding. In addition to physically eliminating the factors as such, a program for correcting measurements in response to disturbance factors has also been established.
In contrast to the foregoing error factors, wind pressure and air flow are sudden and often have an effect as an abrupt change in a weighing device capable of minute mass measurement, and thus a correction processing by a program for elimination of measurement errors is virtually impossible. Therefore, there have been proposed various windproof mechanisms for minimizing the effect of wind pressure and air flow on a weighing mechanism section for measuring the mass.
Air fluctuations as error factors in mass measurement include wind pressure that can be partially perceived as sound and air flow. In particular, the air flow of these is unstable and is longer in time than the wind pressure inmost cases. For example, in an operation to place a sample into a weighing chamber in a weighing device having a weighing chamber, the operation itself inevitably causes air flow, and the air flow has an effect on, for example, the weighing dish and load transfer mechanism to produce measurement errors. The air flow, not at all perceivable by a device user, frequently acts on the weighing device as a factor in producing measurement errors.
Moreover, when the temperature of the weighing chamber has risen higher than that of the outside of the device due to heat generated from an electronic substrate etc., even if the difference in temperature is very slight, air flow occurs when the weighing chamber is opened and closed, and in the case of a liquid sample, slight heat of vaporization generated when the liquid vaporizes or a slight fall in temperature of the liquid due to vaporization and the like also serves as a factor in causing air flow. It has been confirmed that the value of measurement errors due to the air flow reaches 10 mg when it is large. This value equals 100dig in a weighing device with a minimum display of 0.1 mg, which is equivalent to 10000dig in a 1 μg-weighing device, and serves as a major factor in measurement errors.
Because it is considerably difficult to address by a program the effect of measurement errors that incidentally occur due to air fluctuations, in particular, air flow as in the above, various mechanisms for reducing the effect of air flow on the weighing mechanisms, specifically, windproof mechanisms, have been proposed mainly by providers of devices for measuring minute mass such as electronic balances, but each mechanism has both advantages and disadvantages.
The following are patent documents that propose windproof structures.    Patent Document 1: Japanese Utility Model Registration No. 2502949    Patent Document 2: Japanese Published Unexamined Utility Model Application No. S59-062519    Patent Document 3: Japanese Published Examined Utility Model Application No. H07-014825